This invention relates to an electronically controlled automatic transmission in which the time of a shift is automatically adjusted so as to always be held within a set optimum shift time.
In both hydraulically controlled automatic transmissions and electronically controlled automatic transmissions, the time of a shift is decided by such factors as the volume of the chamber of the friction elements [(amount of stroke).times.(area)], orifice diameter for deciding flow rate when oil is applied to the friction elements, and accumulator spring pressure for deciding the slope of hydraulic pressure rise at engagement. Furthermore, since the time of a shift is also influenced by the transmitted torque, the abovementioned parameters are set to respective optimum values in accordance with the engine of the vehicle. Moreover, even if the set values are the same, each of the parameters includes a significant dispersion element. By adopting a method in which the tolerance of orifice diameter is strictly controlled or in which separator plates are selected and assembled from among plates having plural varieties of thicknesses, the time of a shift is held within standards to assure the appropriate shift sensation and durability of the friction elements.
In order to assure an appropriate shift sensation and the durability of the friction elements in the above-described conventional method, manufacturing tolerance is strictly controlled or the amount of stroke is adjusted by selective assembly in the manufacturing process. As a result, the manufacturing process is complicated and the costs involved are high. Moreover, even if the shift time falls within standards due the aforementioned adjustment at the time of manufacture, the shift time may change due to the temperature of the oil in the transmission or the aging of the friction elements. This can have a deleterious effect upon shift sensation and reduce the durability of the friction elements. There are no means for dealing with these problems in the prior art.